Electrically conductive oxide semiconductors have in recent years attracted attention as materials for forming optically transparent, transparent electrodes or an active (channel) layer of thin-film transistors (abbreviation: TFT) or other semiconductor devices (see Patent Documents 1 to 7). Thin-film transistors have been applied to liquid crystal display (abbreviation: LCD) devices and organic electro-luminescent (abbreviation: EL) devices, and utilize an oxide semiconductor as the active channel layer. Moreover, transparent electrodes containing an oxide semiconductor as a component have been applied to display panels such as two-dimensional and three-dimensional display devices, touch panels for mobile communication equipment, and so on.
In order to reduce RC delay of signal transmission, among other purposes, the electrodes and interconnections for oxide semiconductors are formed of metal materials of high electrical conductivity and low electrical resistance. Conventionally, they have been formed from, for example, aluminum (element symbol: Al) or titanium (element symbol: Ti) (see Non-patent document 1), or from molybdenum (element symbol: Mo) (see Non-patent document 1). Further, electrodes and interconnections formed by laminating dissimilar metal layers of alloys of titanium or aluminum and silicon (element symbol: Si) are in use (see Patent Document 1). Recently, a technique has come to be known that forms oxide semiconductor electrodes from copper (element symbol: Cu) which has low electrical resistance (see Patent document 8).
For example, thin-film transistors utilized in liquid crystal display devices (abbreviation: LCD) and the like use copper alloy ohmic electrodes for a source electrode and a drain electrode, along with copper interconnections (see Patent documents 8 and 9). Patent document 10 teaches a technique that uses a copper alloy which has a suitable additive element to Cu and forms a metallic oxide film of the additive element so as to inhibit oxidation of the copper, thereby realizing ohmic electrodes of low electrical contact resistance and copper interconnections of small RC delay. The aforesaid suitable additive element is a metal whose energy of oxide formation is lower than that of copper, and manganese (element symbol: Mn) is given as an example (see Patent document 10).
Non-patent document 3 teaches a technique for forming an electrode made of copper (copper electrode) on a thin-film transistor that uses an electrically conductive oxide semiconductor as an active (channel) layer. Specifically, it is a technique for using copper-manganese (Cu—Mn) alloy to form a copper electrode on a thin-film transistor that uses an amorphous indium-gallium-zinc composite oxide (abbreviation: IGZO) semiconductor layer as the active layer (see Non-patent document 3). It is known that when copper-manganese is used to form a copper electrode on an indium-containing oxide semiconductor like IGZO, a manganese oxide layer is formed at a bonding region of the oxide semiconductor and the copper electrode (see Non-patent document 3).